Cascade electrocatalytic reduction of carbon dioxide and nitrate to ethylamine
Cascade electrocatalytic reduction of carbon dioxide and nitrate to ethylamine
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DOI：
10.1016/j.jechem.2021.06.007
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发表时间：
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影响因子：
13.1
通讯作者：
Zixu Tao;Yueshen Wu;Zishan Wu;Bo Shang;Conor L. Rooney;Hailiang Wang
中科院分区：
文献类型：
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作者：
Zixu Tao;Yueshen Wu;Zishan Wu;Bo Shang;Conor L. Rooney;Hailiang Wang
人们探索了二氧化碳利用，包括将二氧化碳电化学还原为燃料和有用的化学品，以稳定碳排放[1-12]。 CO2电还原产物的价值来源于它们的C−H、CC−C和C−O键。为了进一步提高价值并扩大产品范围，需要将C−N键的形成与CO2的电化学还原结合起来。其中一种可能性是将硝酸盐 (NO3−) 作为反应物，其在水中的过量存在会对饮用水造成风险并导致富营养化等地质问题 [13, 14]。 CO2 和 NO3− 或 NO2− 的共还原最初在几十年前进行了研究，并发现尿素是 CN−N 的产物 [15-18]。最近的努力包括在尿素电合成中用 N2 代替 NO3−，以及使用氨 (NH3) 或胺作为氮源，从 Cu 催化的 CO2 还原的烯酮中间体生成乙酰胺 [19, 20]。此外，我们最近开发了一种电催化反应，能够通过负载在碳纳米管上的分子钴催化剂实现 CO2 和 NO3− 的共还原来合成甲胺 [21]。该级联反应的关键步骤是通过甲醛（HCHO）和羟胺（NH2OH）之间的自发缩合反应形成甲醛肟，甲醛（HCHO）和羟胺（NH2OH）分别是相应电化学CO2和NO3−还原反应的中间体。这一初步成功启发我们探索从廉价且丰富的无机反应物（如 CO2 和 NO3−）直接电合成乙胺，乙胺是化学合成和药物化学中广泛使用的脂肪胺 [22]。在此，我们报告了 CO2 和 NO3− 到乙胺的首次电化学转化，这是一个 20 电子 21 质子还原级联（图 1）。该反应在环境条件下、在氧化物衍生的铜纳米颗粒的催化下、在近中性的水性电解质中进行（图1a）。乙醛肟被认为是乙胺的关键中间体（图1b），是由乙醛（CO2还原为乙醇的活性反应中间体）和NH2OH（NO3−还原为NH3的活性反应中间体）之间的缩合反应形成的。乙醛肟的进一步还原得到最终产物，即乙胺。机理分析表明乙胺的总产率主要受到乙醛竞争性还原为乙醇和NH2OH还原为NH3的限制。
CO2 utilization, including electrochemical reduction of CO2 to fuels and useful chemicals, is explored to valorize carbon emissions [1–12]. The value of CO2 electroreduction products originates from their C− H, C− C, and C− O bonds. To further increase the value and expand the scope of products, it is desirable to integrate C− N bond formation with the electrochemical reduction of CO2. One of such possibilities is to include nitrate (NO3−) as a reactant, whose excessive presence in water can pose risk to drinking water and cause geological issues such as eutrophication [13, 14]. The co-reduction of CO2 and NO3− or NO2− was initially studied several decades ago and urea was found to be the C− N product [15–18]. More recent efforts include replacing N2 for NO3− in the electrosynthesis of urea and using ammonia (NH3) or amines as the N source to generate acetamides from the ketene intermediate of the CO2 reduction catalyzed by Cu [19, 20]. In addition, we have recently developed an electrocatalytic reaction that is able to synthesize methylamine from the co-reduction of CO2 and NO3− enabled by a molecular cobalt catalyst loaded on carbon nanotubes [21]. The key step of this cascade reaction is the formation of formaldoxime by the spontaneous condensation reaction between formaldehyde (HCHO) and hydroxylamine (NH2OH), which are intermediates of the corresponding electrochemical CO2 and NO3− reduction reactions respectively. This initial success inspired us to explore the direct electrosynthesis of ethylamine, which is a widely used aliphatic amine in chemical synthesis and pharmaceutical chemistry [22], from cheap and abundant inorganic reactants such as CO2 and NO3−.Herein, we report the first electrochemical conversion of CO2 and NO3− to ethylamine, a 20-electron 21-proton reduction cascade (Fig. 1). The reaction proceeds under ambient conditions in a near-neutral aqueous electrolyte catalyzed by oxide-derived Cu nanoparticles (Fig. 1a). Acetaldoxime is identified as the key intermediate to ethylamine (Fig. 1b) and is formed from the condensation reaction between acetaldehyde, an active reaction intermediate for CO2 reduction to ethanol, and NH2OH, an active reaction intermediate for NO3− reduction to NH3. Further reduction of acetaldoxime leads to the final product, ie ethylamine. Mechanistic analysis indicates that the overall yield of ethylamine is most limited by the competing reduction of acetaldehyde to ethanol and NH2OH to NH3.